FIG. 3.

Tempo of the neurological disease induced by FrCas^NC, FC70, CFC, and CF223. Mice were inoculated intraperitoneally on postnatal day 1 and observed for signs of neurological disease. As was done in Fig. 1B, clinical disease here was divided into the mild neurological signs (A) and severe late signs (B). Mice inoculated with FrCas^NC (n = 38), FC70 (n = 32), and CFC (n = 34) all exhibited rapid onset of mild neurological signs, whereas these signs were delayed in mice inoculated with CF223 (n = 18). The tempo of paralysis and wasting, however, brought out in more striking terms the differences in neurovirulence of these viruses. Only FrCas^NC induced rapidly progressive paralysis. Paralysis was seen in all of the FC70-inoculated mice but was delayed compared to FrCas^NC. Only 25% of the mice inoculated with CFC exhibited paralysis and wasting. None of the mice inoculated with CF223 developed paralysis over the 100-day observation period.